Conventionally two signal lines have been required for communicating two types of data bidirectionally between pieces of equipment. One of the communication lines is a signal line for transmission. The other communication line is a signal line for reception.
Moreover, in Patent Literature 1, there has been proposed a technique of performing transmission of two types of data by one signal, using an open collector circuit between pieces of equipment. In Patent Literature 1, a direction where the data is communicated is unidirectional. In Patent Literature 1, a thermistor is attached to a collector that the open collector circuit has. In a communication circuit disclosed in Patent Literature 1, a voltage at off time is detected in a reception-side circuit to thereby perform the transmission of the two types of data. The two types of data are encoder position information and temperature information.